Abstract

Fifty three cultures belonging to different species and groups as recognised in the existing system of classification of the genus Fusarium and one culture of Helminthosporium sativum were classified by a numerical (Adansonian) method. A total of 160 characters was studied; these included morphological, cultural, physiological, pathological and biochemical features. Only those tests which discriminated between the different strains were used in the computer analysis; omission of characters which were either positive or negative for all the strains reduced the number of features for computation from 160 to 132. The analysis of data on the properties of all the fungal strains was carried out using University of Surrey computer No. ICL 1905 F, according to Adansonian principles of classification as developed by Sneath (1957b). Two methods of grouping, single link grouping (S.L.G.) and single link listing (S.L.L.) were used; dendrograms and similarity matrices were constructed. The computer calculated value (percentage similarity) "S", ranged from 72.3 to 92.1 percent by the S.L.G. method and from 65.7 to 92.8 percent by the S.L.L. method. Groupings obtained by the S.L.G. method were more elaborate at a given level of similarity than those from the S.L.L. method and were therefore chosen for defining groups. The similarity at a level of 80. 2% was selected for defining groups by the S.L.G. method, since at this level 41 of the 54 isolates were joined together within 8 groups. The computer-defined groups were generally more similar to those of the two most widely used systems of classification in Fusarium taxonomy. In order to assess the value of different categories of characters in forming groups of Fusarium isolates, a separate analysis was made of the morphological and cultural, physiological, pathological and biochemical characters. Dendrograms were constructed and compared with the main dendrogram in which all available characters were used.